1. SINGLE PHASE
INDUCTION MOTOR

2. The single phase induction machine is the most frequently used motor for refrigerators, washing machines, clocks, drills, compressors, pumps and so on.
The single phase motor stator has a laminated iron core with two windings arranged perpendicularly.
One is the main
The other is the auxiliary winding or starting winding

4. This single phase motors are truly two phase machines.
The motor uses a squirrel cage rotor, which has a laminated iron core with slots.
Aluminum bars are molded on the slots and short-circuited at both ends with a ring.
Figure 1: Single phase induction motor

5. Figure 2: Squirrel cage rotor

6. The single-phase induction motor operation can be described by two methods:
Double revolving field theory
Cross field theory
Double revolving theory is perhaps the easier of the explanations to understand.

7. Double revolving field theory
A single phase ac current supplies the main winding that produces a pulsating magnetic field.
Mathematically, the pulsating field could be divided into two fields, which are rotating in opposite directions.
The interaction between the fields and the current induced in the rotor bars generates opposing torque.

8. The interaction between the fields and the current induced in the rotor bars generates opposing torque.
Under these conditions, with only the main field energized the motor will not start.
However, if an external torque moves the motor in any direction, the motor will begin to rotate.
Figure 3: Single phase motor main winding generates two rotating fields, which oppose and counter balance one another.

9. The pulsating filed is divided a forward and reverse rotating field.
Motor is started in the direction of forward rotating field this generates small (0.5%) positive slip.
Reverse rotating field generates a larger (1.95%) negative slip

10. Starting Single Phase Induction Motor
The three major starting technique
1. Split phase windings
2. Capacitor type windings
3. Shaded stator poles
Split-phase windings
- A split phase motor is a single phase induction motor with two stator winding, a main stator winding (M) and auxiliary winding (A).
- These two winding are set 90 electrical degrees apart along the stator of the motor.
- The auxiliary winding is design to be switched out of the circuit at some set speed by a centrifugal switch.

11. Capacitor Start Motors
In this motor a capacitor is placed in series with aux winding
By proper selection of capacitor size, the magnetomotive force of the starting current in aux winding can be adjusted to be equal to the magnetomotive force of the current in the main winding and current in aux winding lead current in main winding by 90 degree.
This motor are more expensive than split phase motor and they are used in applications where a high starting torque is absolutely require
Typical application are compressor, pumps and air conditioners

12. Shaded pole motor
Only have main winding.
It has salient pole and one portion of each pole is surrounded by short circuited coil called a shading coil.
Shaded pole produce less starting torque than any type of induction motor starting system.
They are less efficient and have a much higher slip than other types of single phase induction motors.

13. Speed Control of Single Phase Induction Motor
For squirrel cage rotor motor the following techniques are available
Vary the stator frequency
Change the number of poles
Change the applied terminal voltage
This can be done by
Used an autotransformer
Used SCR or TRIAC circuit
Used a resistor

14. The circuit model of a single phase induction motor
The equivalent circuit of a single phase induction motor at standstill. Only its main windings are energized
The equivalent circuit with the effects of the forward and reverse magnetic fields separated

15. Circuit analysis with the single phase induction motor equivalent circuit
The equivalent circuit of a single phase induction motor running at a speed with only its main winding energized

16. In term of ZF and ZB, the current flowing in the induction motor’s stator winding is
The air gap power for the forward magnetic field
The air gap power for reverse magnetic field

17. Total air gap power
Induced torque
Rotor copper losses
Forward rotor copper losses
Reverse rotor copper losses

18. The power converted from electrical to mechanical
Since
This equation can be expressed as

19. Assignment
A 1kW, 240V, 50Hz, 4 pole, split-phase induction motor has the following impedances:
R1 = X1 = 2.10 XM= 58.2
R2 = X2 = 1.56
The core losses of this motor are 60W and the friction and stray losses are 32W. The motor is operating at the rated voltage and frequency with its starting winding open and the motor slip is 6.0 %. Find the following quantities in the motor at these conditions:
1. The equivalent circuit Total air gap power
2. ZF and ZB Pconv
3. Speed in rpm Induced torque
4. Stator current Output power
5. Stator power factor Load torque
6. Input power Efficiency